21209321 has 8 divisors (see below), whose sum is σ = 24267264. Its totient is φ = 18158400.

The previous prime is 21209317. The next prime is 21209327. The reversal of 21209321 is 12390212.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21209321 - 2² = 21209317 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21209293 and 21209302.

It is not an unprimeable number, because it can be changed into a prime (21209327) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 9896 + ... + 11846.

It is an arithmetic number, because the mean of its divisors is an integer number (3033408).

Almost surely, 2^21209321 is an apocalyptic number.

It is an amenable number.

21209321 is a deficient number, since it is larger than the sum of its proper divisors (3057943).

21209321 is a wasteful number, since it uses less digits than its factorization.

21209321 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3511.

The product of its (nonzero) digits is 216, while the sum is 20.

The square root of 21209321 is about 4605.3578579737. The cubic root of 21209321 is about 276.8060565976.

Adding to 21209321 its reverse (12390212), we get a palindrome (33599533).

The spelling of 21209321 in words is "twenty-one million, two hundred nine thousand, three hundred twenty-one".